Multicolor diffusion transfer process employing a minimum amount of a processing composition



Dec. 23. 1969 H. LAND 3,485,628

MULTICOLOR DIFFUSION TRANSFER PROCESS EMPLOYING A MINIMUM AMOUNT OF APROCESSING COMPOSITION Filed July 15, 1965 3 Sheets-Sheet 1 VSUPPORTLAYER CONTAINING NON- DIFFUSIBLE ACID-REACTING REAGENT |-SPACER LAYER-|MAGE-RECEIVING LAYER I-BLUE-SENSITIVE SILVER HALIDE YELLOw DYEDEVELOPER -SPACER LAYER GREEN-SENSITIVE SILVER HALIDE L-MAGENTA DYDEVELOPER L/SPACER LAYER -RED-SENSITIVE SILVER HALIDE -CYAN DYEDEVELOPER INVENTOR QMW XML FIG. 2

ATTORNEYS MULTICOLOR DIFFUSION TRANSFER PROCESS EMPLOYING A MINIMUMAMOUNT OF A PROCESSING COMPOSITION Filed July 13, 1965 3 Sheets-Sheet 2Dec. 23. 1969 E H. LAND 3,485,628

GREEN BLUE RED LOG E AJJSNBO INVENTOR- 5M K M WJ ATTORNEYS E. H. LANDDec. 23. 1969 MULTICOLOR DIFFUSION TRANSFER PROCESS EMPLOYING A MINIMUMAMOUNT OF A PROCESSING COMPOSITION Filed July 13, 1965 3 Sheets-Sheet 5SE Illl M53 i 235 0 N Y. Q. m o um AJJSNHO AT ORNEYS 3,485,628MULTICOLOR DIFFUSION TRANSFER PROCESS EMPLOYING A MINIMUM AMOUNT OF APROC- ESSING COMPOSITION Edwin H. Land, Cambridge, Mass, assignor toPolaroid Corporation, Cambridge, Mass., a corporation of Delaware FiledJuly 13, 1965, Ser. No. 471,665 The portion of the term of the patentsubsequent to Jan. 9, 1985, has been disclaimed Int. Cl. G )3c 5/54,7/00 11.5. Cl. 96-29 12 Claims ABSTRACT OF THE DISCLOSURE Diffusiontransfer color images are formed by a process wherein a small quantityof processing liquid is absorbed into an exposed photosensitive element,and the wetted photosensitive element is then superposed on a dryimage-receiving element which includes a non-diffusible, acid-reactingreagent positioned in a layer adjacent the image-receiving layer, Thequantity of processing liquid absorbed by the exposed photosensitiveelement is sufficient to effect development and transfer.

This invention relates to photography and, more particularly, to amethod of forming improved photographic images in dyes by diffusiontransfer processes.

US. Patent No. 2,983,606, issued May 9, 1961 to Howard G. Rogers,discloses diffusion transfer processes employing dye developers to formcolor transfer images. The copending application of Edwin H. Land andHoward G. Rogers, Ser. No. 565,135, filed Feb. 13, 1956 (now US. PatentNo. 3,345,163 issued Oct. 3, 1967), discloses the use of such dyedevelopers in integral multilayer negatives to give multicolor transferimages. This invention is particularly concerned with an improvement insuch dye developer diffusion transfer processes and, it is a primaryobject of this invention to provide novel diffusion transfer processeswhereby dye developer transfer images are obtained which exhibitunobvious and superior photographic quality.

It is a further object of this invention to provide a novel diffusiontransfer process employing a nonviscous processing composition.

A further object of this invention is to provide diffusion transferprocesses wherein a processing composition is allowed to act upon anexposed photosensitive element for a predetermined period prior tosuperposing said exposed photosensitive element on a dry image-receivingelement, which image-receiving element includes a nondiffusible,acid-reacting reagent positioned in a layer adjacent the image-receivinglayer.

Yet another object of this invention is to provide diffusion transferprocesses wherein a minimum quantity of processing composition isemployed to effect development and transfer.

A further object of this invention is to provide diffusion transferprocesses for forming multicolor transfer images having increased dyedensity and improved color reproduction.

Still another object of this invention is to provide a novel diffusiontransfer process which employes a highly alkaline, nonviscous processingcomposition, and wherein the pH of the color transfer image issubstantially reduced very rapidly prior to exposing the image dyes toair and will in part appear hereinafter.

The invention accordingly comprises the processes m- Other objects ofthe invention will in part be obvious 1 it aired States Patent O"'"icePatented Dec. 23, 1969 volving the several steps and the relation andorder of one or more of such steps with respect to each of the otherswhich are exemplified in the following detailed disclosure and the scopeof the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic enlarged cross-sectional view illustratingthe processing of a photosensitive element in a preferred embodiment ofthis invention;

FIG. 2 is a diagrammatic enlarged cross-sectional view of aphotosensitive element in face-to-face contact with an image-receivingelement in a preferred embodiment of this invention;

FIG. 3 is a graphic illustration of the transfer density versus exposurerelationship of each dye in a multicolor dye developer transfer imageobtained in accordance with this invention, wherein the image-receivingelement contains a layer of a polymeric acid; and

FIG. 4 is a graphic illustration of the transfer density versus exposurerelationship of each dye in a multilayer dye developer transfer imageformed in the same manner as the image from which the curves reproducedin FIG. 3 were obtained, except that the image-receiving element did notcontain a layer of a polymeric acid.

The above-mentioned US. Patent No. 2,983,606 and copending applicationSer. No. 565,135, disclose highly useful diffusion transfer processeswhich employ dye developers. As set forth therein, and in numerous otherpatents, a dye developer is a compound which is both a dye and a silverhalide developing agent. Particularly useful and preferred dyedevelopers are azo and anthraquinone dyes which contain one or morehydroquinonyl groups. Numerous examples of useful dye developers andsyntheses for preparing dye developers have been set forth in theliterature and such information, therefore, is omitted from thisapplication.

The dye developer diffusion transfer process has been embodied incommercially available films intended for use in self-developing camerasto obtain a full color transfer image in approximately one minute. Inthese films, the processing composition is supplied in a highly viscousform, and it is applied to the exposed photosensitive element by beingspread between said exposed photosensitive element and animage-receiving element as said elements are brought into superposedrelationship. The image-receiving element contains a non-diffusible,acid-reacting reagent positioned in a layer adjacent the image-receivinglayer; image-receiving elements of this type and color diffusiontransfer processes employing such image-receiving elements are disclosedand claimed in the copending application of Edwin H. Land, Ser. No.234,- 864, filed Nov. 1, 1962 (now US. Patent No. 3,362,819 issued Jan.9, 1968). The aforementioned non-diffusible, acid-reacting reagent iseffective to substantially reduce the pH of the color transfer imageprior to the time at which the photosensitive element and theimage-receiving element are separated from their superposedrelationship, thereby eliminating post-treatment of said separatedimagereceiving element to avoid color changes due to exposing the imagedyes to the air. Diffusion transfer images formed on image-receivingelements containing such a non-diffusible, acid-reacting reagent exhibithigh optical clarity and luminosity.

The aforementioned US. Patent No. 2,983,606 and copending applicationSer. No. 565,135, recognize that the processing composition may beapplied to the exposed photosensitive element before said exposedphotosensitive element is brought into superposed relationship with theimage-receiving element. In addition, it is disclosed that suchdiffusion transfer processes may be practiced without the use of afilm-forming, i.e., viscosity-increasing material, such as sodiumcarboxymethyl cellulose or hydroxyethyl cellulose, in the processingcomposition.

It now has been discovered that the efficiency of such diffusiontransfer processes as well as the quality of the resulting colortransfer image may be substantially improved by treating the exposedphotosensitive element with a processing composition for a predeterminedperiod, during which period the photosensitive element absorbs arelatively small quantity of processing solution, and thereafterbringing said exposed photosensitive element into face-to-face contactwith a dry image-receiving element containing a non-diffusible,acid-reacting reagent positioned in a layer adjacent the image-receivinglayer. Multicolor transfer images formed in accordance with thisinvention have been found to exhibit improved density and color qualityas compared with multicolor transfer images obtained by use of thenonviscous processing composition with a dry image-receiving elementwhich does not contain said nondilfusible, acid-reacting reagent. Thediffusion transfer processes of this invention are characterized by thefact that an extremely small quantity of processing solution is employedto process each frame or negative.

In the preferred embodiments of this invention, the processing solutionis absorbed into the exposed photosensitive element from a nonviscousprocessing solution, e.g., by passing the exposed photosensitive elementthrough a container of said processing solution. Other techniquescapable of supplying the requisite small quantity of processing solutionsubstantially uniformly over the negative area also may be used, e.g., aliquid applicator which provides a capillary interspace through whichthe processing solution is applied, as disclosed in my copendingapplication Ser. No. 242,271, filed Nov. 8, 1962 (now US. Patent No.3,194,138 issued July 13, 1965). It is also possible to have thephotosensitive element absorb the requisite quantity of processingsolution from a viscous processing composition, provided it is appliedin such a way that no layer of polymer or processing composition ispresent between the subsequently superposed photosensitive element andimage-receiving element. The use of a nonviscous processing solution.however, is preferred, since it permits one to employ very simpleprocessing apparatus and handling techniques. It will be noted that,regardless of the particular technique of supplying the processingsolution to the photosensitive element, the image-receiving element iskept dry until it is brought into faceto-face contact With the wettedphotosensitive element, and thus the image-receiving element is wettedessentially only by processing solution extracted from thephotosensitive element.

The expression face-to-face contact is used herein to denote the absenceof any layer of processing composition between the superposedphotosensitive element and imagereceiving element.

As used herein ,the expressions nonviscous processing solution andnonviscous processing composition are intended to refer to processingsolutions or compositions having a viscosity substantially the same asthat of water. The nonviscous processing composition does not contain apolymeric film-forming material or other viscosityproviding componentsuch as that employed in the commercially practiced color diffusiontransfer process. In general, one may obtain nonviscous processingsolutions suitable for use in this invention by simply omitting thefilm-forming reagent from processing compositions of the typesheretofore described in the literature; in certain instances suchviscous processing compositions also may contain a reagent whose primaryfunction is to facilitate the adherence of the partially solidifiedlayer of processing composition to either the exposed photosensitiveelement or image-receiving element when said elements are separated fromtheir superposed relationship, and such reagent also may be omittedsince this function is not utilized in the process of the instantinvention. In some instances, the novel processing techniques of thisinvention have permitted a reduction in the concentration of one or morereagents of the processing composition as compared with theconcentration of said reagent which would be employed in a viscousprocessing composition. The particular concentration of a given reagentwhich should be employed in a nonviscous processing composition may bereadily determined by one skilled in the art by performing routineconcentration tests.

As noted above, a nonviscous processing composition may be applied tothe photosensitive element by a number of techniques, e.g., by use of aporous applicator block or head, by dipping the exposed photosensitiveelement into a container of the nonviscous processing composition or bypassing the exposed photosensitive element through a container of saidnonviscous processing composition. Particularly useful apparatus forpracticing the processes of this invention and embodying the latter twotechniques are disclosed in the copending application of Edwin H. Landand Vaito K. Eloranta, Ser. No. 509,957 filed Nov. 26, 1965, and thecopending application of Edwin H. Land and Albert J. Bachelder, Ser. No.509,713 filed Nov. 26, 1965.

Referring to the drawing, FIG. 1 shows an exposed photosensitive element1 (containing absorbed processing solution) being removed from acontainer 5 of a nonviscous processing solution 7 and being brought intoface-to-face contact with a dry image-receiving element 3 by passingsaid elements between pressure rolls 9 and 11. It will be noted that thepressure rolls 9 and 10 may be of much simpler construction and mountingthan would be the case if the rolls were required to distribute aviscous processing liquid between the two sheets, since the pressurerolls 9 and 11 are required only to press the photosensitive element 1and the image-receiving element 3 into face-to-face contact with eachother. Squeegees or other means (not shown) may be provided to removeexcess processing solution adhering to the front and/or back of thephotosensitive element as it is withdrawn from the processing solution 7prior to being superposed on the dry image-receiving element.

The preferred structures of the image-receiving element and thephotosensitive element are shown in superposed relationship and ingreater detail in 'FIG. 2. Imagereceiving element 3 comprises a support21 bearing a layer 23 containing a non-difiusible, acid-reactingreagent, a spacer layer 25, and an image-receiving layer 27. Thephotosensitive element 1 comprises a support 31 carrying a layer 33 of acyan dye developer, a layer 35 of a red-sensitive silver halideemulsion, a spacer layer 37, a layer 39 of a magenta dye developer, alayer 41 of a green-sensitive silver halide emulsion, a spacer layer 43,a layer 45 of a yellow dye developer, and a layer 47 of a blue-sensitivesilver halide emulsion. In certain instances, the blue-sensitiveemulsion layer may be overcoated with a layer containing an auxiliarysilver halide developing agent, as disclosed and claimed in US. PatentNo. 3,192,044 issued June 29, 1965 to Howard G. Rogers and Harriet W.Lutes.

By way of recapitulation, this invention provides a transfer processwherein a photosensitive element is allowed to absorb a predetermined,small quantity of processing solution, after which it is brought intofaceto-face contact with a dry image-receiving element containing anon-diffusible, acid-reacting reagent in a layer of the image-receivingelement adjacent to the imagereceiving layer. The requisite quantity ofprocessing solution is absorbed by allowing the photosensitive elementto be in contact for a predetermined period with an appropriate quantityof processing composition, e.g., a container of a nonviscous processingsolution. This predetermined period constitutes, as a minimum, a periodof time sufiicient for the permeable layers of said photosensitiveelement, or at least some of such permeable layers, to absorb from saidprocessing composition a quantity of processing solution sufficient toeffect diffusion transfer processing of said photosensitive element,and, as a maximum, a period of time after which the unoxidized dyedevelopers would begin to diffuse laterally and/ or out of thephotosensitive layer, prior to bein superposed on the dryimage-receiving element, to an extent such that the photographic qualityof the transfer image (particularly such elements of photographicquality as maximum density, color saturation and color separation) wouldbe adversely affected. It will be recognized that the practical limitsof this predetermined period will vary as a function of the permeabilityand swellability of the various layers and hence the rate at which theprocessing solution or liquid is absorbed, the diffusion rates of thedye developers, etc., and may be readily and quickly determined by oneskilled in the art for any given combination of photosensitive element,image-receiving element and viscous processing liquid. It will also berecognized that it is within the ability of one skilled in the art tovary such permeability and/or dilfusibility to facilitate practice ofthis processing technique. Thus, for example, one may reduce the initialrate of diffusion by employing hydrolyzable derivatives of dyedevelopers, as disclosed and claimed in the copending application ofEdwin H. Land and Howard G. Rogers, Ser. No. 194,359, filed May 14, 1962(now US. Patent No. 3,- 230,082 issued Ian. 18, 1966).

While the precise reasons for the improved efficiency and color qualityobtained in the processes of this invention are not fully understood,certain factors may be identified. Initially, it will be noted that avery small quantity of processing solution is absorbed into thenegative, and that absorbed liquid is allowed to act only upon theexposed negative for a controlled period prior to the superpositioningthereon of the dry image-receiving element. Because the image-receivingelement is dry, it acts as a sink, i.e., it starts to extract processingsolution from the negative at a rapid rate. There is no reservoir ofprocessing solution between the superposed negative and image-receivingelement, as there is when a viscous processing solution is employed. Therapid extraction absorption of processing solution from the negative bythe dry image-receiving element, together with the attraction of theditfusible dye developers to the mordant and/or dyeable materials of theimage-receiving layer, accelerates the transfer of diffusible dye to theimagereceiving element. In addition, the time controlled changes inconcentration gradients which are created by this processing techniqueminimize the natural tendency of the yellow and magenta dye developersto diffuse inwardly towards the base of the photosensitive element, thusreducing the loss of transfer density and the creation of undesirableinter-image effects which flow from such inward diffusion of dyedevelopers. Because the imagereceiving element is not brought intosuperposed relationship with the wetted negative until after therequisite quantity of processing solution has been absorbed into thenegative, there is a delay before the acid-reacting reagent is availableto react with alkali dissolved in the processing solution, without acorresponding delay in the ability of the processing solution toinitiate development of the photosensitive element. Once theacid-reacting reagent does have access to the alkaline components of theprocessing solution, it is effective to reduce the pH at a more rapidrate, in view of the small total quantity of processing solution beingused, than if it is used with a viscous processing composition appliedsimultaneously to both the negative and the image-receiving element.Thus, the pHreducing action of the acid-reacting reagent is deferredwithout having to lower the rate at which pH reduction is effected onceit is initiated. In addition, the reaction of the alkali with apolymeric acid, as in the preferred embodiments, releases a quantity ofwater which, though quite small, is significant in relation to the totalquantity of processing solution originally absorbed into thephotosensitive element. This released Water of reaction is formedimagewise and is believed to aid in the desired transfer of thediifusible dyes. One other factor may be mentioned: image-receivingelements containing a polymeric acid layer are appreciably thicker thansimilar elements which do not contain such a polymeric acid layer; thisadded thickness of permeable layers of the image-receiving element alsois believed to have an effect in creating the desired time controlledchanges in the concentration gradients of the various reagents,including the alkali and the diffusible dye developers.

The several patents and copending applications referred to herein, inaddition to other issued patents, disclose a number of integralmultilayer negatives which may be employed in the practice of thisinvention. In general, these multilayer negatives have a structure ofthe type shown in FIG. 2. The dye developer layers are prepared bydissolving each dye developer in a water-immiscible solvent anddispersing the resulting solution in gelatin. Unless otherwiseindicated, the negatives employed in the examples given herein alsocontain a small quantity of 4-methylphenyl-hydroquinoue dispersed in alayer of gelatin coated over the blue-sensitive silver halide emulsion.

As noted above, the image-receiving element includes a layer containinga non-diffusible, acid-reacting reagent. In the preferred embodiments ofthis invention, a layer containing an acid-reacting polymer, andparticularly a polymer containing free carboxyl O (&-OH) groups, isprovided between the image-receiving layer [i.e., the layer in which thedye image is formed, and frequently referred to simply as the imagelayer] and the support. For simplicity, this layer is sometimes refererdto herein as a polymeric acid layer or as an acid polymer layer.

The pH of the processing composition preferably is at least 12, and morepreferably is of the order of at least 13 to 14. The acid polymer layercontains at least sufficient acid groups to effect a reduction in the pHof the image layer from a pH of about 12 or 13 to 14 to a pH of at least11 or lower at the end of the imbibition period, and preferably to a pHof about 5 to 8 within a short time after imbibition.

It is, of course, necessary that the action of the polymeric acid be socontrolled as not to interfere with either development of the negativeor image transfer of unoxidized dye developers. For this reason, the pHof the image layer should be kept at a level of pH 12 to 14 until thepositive dye image has been formed after which the pH should be reducedvery rapidly to at least about pH 11, and preferably about pH 8 to 10,before the positive image is separated and exposed to air. Unoxidizeddye developers containing hydroquinonyl developing radicals diffuse fromthe negative to the positive as the sodium, potassium or other alkalisalt. The diffusion rate of such dye developers thus is at least partlya function of the alkali concentration, and it is necessary that the pHof the image layer remain on the order of 12 to 14 until transfer of thenecessary quantity of dye developer has been accomplished. Thesubsequent pH reduction serves a highly valuable photographic functionby substantially teminating further dye transfer, thus effectivelyminimizing changes in color balance as a result of longer imbibitiontimes in multicolor processes using multilayer negatives.

In order to prevent premature pH reduction evidenced, for example, by anundesired reduction in positive image density, the acid groups are sodistributed in the acid polymer layer that the rate of theiravailability to the alkali is controllable, e.g., as a function of therate of swelling of the polymer layer, which rate in turn has a directrelationship to the diffusion rate of the alkali ions. The desireddistribution of the acid groups in the acid polymer layer may beeffected by mixing the acid polymer with a polymer free of acid groups,or lower in concentration of acid groups, and compatible therewith, orby using only the acid polymer but selecting one having a relativelylower proportion of acid groups. These embodiments may be illustrated,respectively, by (a) a mixture of cellulose acetate and celluloseacetate hydrogen phthalate and (b) a cellulose acetate hydrogenphthalate polymer having a much lower percentage of phthalyl groups thanthe first-mentioned cellulose acetate hydrogen phthalate.

The layer containing the polymeric acid thus may also contain awater-insoluble polymer, preferably a cellulose ester, which acts tocontrol or modulate the rate at which the alkali salt of the polymeracid is formed. As examples of cellulose esters contemplated for use inthis invention, mention may be made of cellulose acetate, celluloseacetate butyrate, etc. Such a polymer also may be added to provideincreased wet adhesion to prevent separation of the image-receivinglayer or other layers of the imagereceiving element during processing.The particular polymers and combinations of polymers employed in anygiven embodiment are, of course, selected so as to have adequate wet anddry strength. Where necessary or desirable, suitable subcoats may beemployed to help the various polymeric layers adhere to each otherduring storage and use.

As used herein, the term polymeric acid is intended to mean polymerswhich contain acid groups, such as carboxylic acid and sulfonic acidgroups, which are capable of forming salts with alkali metals, such assodium, potassium, etc., or with organic bases, particularly quaternaryammonium bases, such as tetramethyl ammonium hydroxide, or potentiallyacid-yielding groups, such as anhydrides or lactones, or other groupswhich are capable of reacting with bases to capture and retain them. Theacid-reacting group is, of course, non-diifusible from the acid polymerlayer. In the preferred embodiments, the acid polymer contains freecarboxyl groups and the processing composition contains a largeconcentration of sodium or potassium ions. The acid polymers found to bemost useful are characterized by containing free carboxyl groups, beinginsoluble in water in the free acid form, and by forming water-solublesodium salts. One may employ polymers containing carboxylic acidanhydride groups, at least some of which preferably have been convertedto free carboxyl groups prior to imbibition. While the most readilyavailable polymeric acids are derivatives of cellulose or of vinylpolymers, polymeric acids from other classes of polymers may be used. Asexamples of specific polymeric acids contemplated as being used in thisinvention, mention may be made of dibasic acid halfester derivatives ofcellulose which derivatives contain free carboxyl groups, e.g.,cellulose acetate hydrogen phthalate, cellulose acetate hydrogenglutarate, cellulose acetate hydrogen succinate, ethyl cellulosehydrogen succinate, ethyl cellulose acetate hydrogen succinate,cellulose acetate hydrogen succinate hydrogen phthalate; ether and esterderivatives of cellulose modified with sulfoanhydrides, e.g., withortho-sulfobenzoic anhydrides; polystyrene sulfonic acid; carboxymethylcellulose; polyvinyl hydrogen phthalate; polyvinyl acetate hydrogenphthalate; polyacrylic acid; acetals of polyvinyl alcohol with carboxyorsulfo-substituted aldehydes, e.g., m-, or pbenzaldehyde sulfonic acid orcarboxylic acid; partial esters of ethylene/maleic anhydridecopolyrners; partial esters of methylvinyl ether/maleic anhydridecopolyrners; etc.

It has also been found that the provision of an inert interlayer betweenthe image layer and the polymeric acid layer substantially improves thecontrol of the pH reduction by the polymeric acid layer. While thisspacer layer preferably is composed of a polymer such as polyvinylalcohol, other polymers, such as gelatin, which are inert to alkali butthrough which the alkali may diffuse to the polymeric acid layer, may beused. The presence of such an interlayer has been found quite effectivein evening out the various reaction rates over a wide range oftemperatures, e.g., by preventing premature pH reduction when imbibitionis effected at temperatures above room temperature, e.g., at 95l00 F. Byproviding an inert interlayer, the rate at which alkali is available forcapture in the polymeric acid layer becomes a function of alkalidiffusion rates. The pH reduction thus is made relatively independent ofchemical reaction rates which would show a greater variation oversimilar wide changes in imbibition temperature.

In a particularly useful embodiment, the spacer layer referred to abovecomprises a polymer which exhibits a permeability to alkali ions whichis inversely temperature dependent, i.e., it exhibits decreasingpermeability to solubilized alkali ions, such as alkali metal andquaternary ammonium ions, under conditions of increasing temperature.The use as spacer layers of polymers which exhibit such inversetemperature dependent permeability to alkali is disclosed and claimed inthe copending application of Leonard C. Farney, Howard G. Rogers andRichard W. Young, Ser. No. 447,100, filed Apr. 9, 1965 and nowabandoned. As examples of such polymers, mention may be made ofhydroxypropyl polyvinyl alcohol. polyvinyl methyl ether, polyethyleneoxide, polyvinyl oxazolidinone, hydroxypropyl methylcellulose, andpartial acetals of polyvinyl alcohol, such as the partial acetals.butyrals, formals and propionals of polyvinyl alcohol. Particularlyuseful partial acetals of polyvinyl alcohol have molecular weights ofabout 1000 to 50,000 and have from about 10 to of the available hydroxylgroups acetalized. Mixed acetals also may be used, and the aldehyde mayitself be substituted, e.g., methoxypropionaldehyde. Mixtures of suchpolymers, e.g., hydroxypropyl methylcellulose and a partial polyvinylbutyral, also may be used. The use of this type of polymmeric spacerlayer has resulted in improved processing results, particularly withrespect to pH control and dye densities, over a wider temperature range,and especially at lower temperatures.

The inert spacer layer, e.g., the polyvinyl alcohol or partial polyvinylbutyral interlayers, acts to time control the pH reduction by thepolymeric acid layer. This timing is a function of the rate at which thealkali diffuses through this inert spacer layer. It has been found thatthe pH does not drop until the alkali has passed through this spacerlayer, i.e., the pH is not reduced to any significant extent by the merediffusion of alkali into the polyvinyl alcohol interlayer, but the pHdrops quite rapidly once the alkali diffuses through the polyvinylalcohol layer.

It is an important feature of the preferred embodiments of thisinvention that the reaction of the polymeric acid with the diffusingalkali releases water. This water of reaction appears to have anaccelerating effect upon the rate at which the pH is reduced. Prior topermeation of the alkali through the inert spacer layer, the equilibriafavor the alkali remaining close to the negative and close to the imagelayer. Once alkali has permeated through to the polymeric acid layer,the equilibria are shifted by the trapping of that alkali. In addition,the water formed by reaction of the acid polymer with the alkali helpsto remove alkali ions from the image layer and helps swell the insertpolymer, thereby increasing the rate at which the alkali diffusesthrough the inert layer to the polymeric acid layer. These factors helpto keep the pH high until the image is formed, and then to cause the pHto drop rapidly after the image has been formed. Thus, the pH may bekept high during development and transfer, and rapidly dropped after thetransfer image has been formed. This also helps to effect the pHreduction within the same imbibition periods which otherwise would beemployed. In additon, the released water of reaction permits thepositive and negative to remain in superposed relationship for muchlonger imbibition times without sticking which is caused by drying out.In turn, this released water permits one to continue imbibition forperiods long enough to assure more than the minimum desired pHreduction. The fact that the pH reduction also acts to create aself-limiting transfer density permits such continued imbibition toproceed without undesired color balance changes.

Particularly good results have been obtained using image-receivinglayers comprising polyvinyl alcohol and poly-4-vinylpridine in ratios,by weight, for example, of from 1:3 to 3:1.

Although a preferred image-receiving layer is such a mixture ofpolyvinyl alcohol and poly-4-vinylpyridine (such receiving layers aredisclosed and claimed in U.S. Patent No. 3,148,061 issued to Howard C.Haas on Sept. 8, 1964), the invention is not limited thereto. Otherimage-receiving layers, such as the partial acetals of polyvinyl alcoholwith trialkylammonium benzaldehyde quaternary salts, e.g., thep-trimethylammonium benzaldehyde p-toluene sulfonate partial acetal ofpolyvinyl alcohol [as disclosed and claimed in the copending applicationof Howard C. Haas, Ser. No. 71,424, filed Nov. 25, 1960] (now U.S.Patent No. 3,239,337 issued March 8, 1966), are known in the art and maybe employed. Similarly, while the preferred embodiment effectsdevelopments in the presence of a quaternary ammonium compound (asdisclosed and claimed in U.S. Patent No. 3,173,786 issued to MiltonGreen and Howard G. Rogers on Mar. 16, 1965), and particularly aquaternary ammonium compound capable of forming an active methylene basein alkali, the invention is not so limited, even though the advantagesare most dramatic when such an active methylene quaternary ammonium saltis used.

The polymeric acid layer is preferably relatively thick as compared,e.g., with the image-receiving layer. The image-receiving layer ispreferably about 0.25 to 0.4 mil thick, and the polymeric acid layer ispreferably 0.5 to 1.5 mil thick. If an inert spacer layer is present,that layer is preferably about 0.1 to 0.7 mil thick. Plasticizers may beadded to one or more layers to increase flexibility, and subcoats may beemployed to facilitate adhesion of various of the layers.

Processing preferably is effected in the presence of an auxiliary oraccelerating silver halide developing agent which is substantiallycolorless, at least in the unoxidized form. Particularly useful aresubstituted hydroquinones, such as phenylhydroquinone,4'-methylphenyl-hydroquinone, toluhydroquinone,tertiary-butyl-hydroquinone, and 2,5-triptycene diol. Thesehydroquinones may be employed as components of the processingcomposition or they may be incorporated in one or more layers of thenegative. Particularly useful results are obtained when 4-methylphenylhydroquinone is dispersed in one or more of the gelatininterlayers of the negative and/or in a gelatin layer coated over theblue-sensitive emulsion layer.

Where desired, the support for the image-receiving layer may betransparent or opaque. Suitable opacifying agents may be incorporated inthe negative and/ or positive to permit imbibition to be completedoutside of a camera, i.e., in an area exposed to light actinic to thesilver halide emulsion. In particularly useful embodiments, the additionof small quantities of a white pigment, such as titanium dioxide, to thepolymeric acid layer, spacer layer, etc., is efifective to prevent edgeleakage of light during processing outside of a camera.

Suitable hardening agents may be employed in the image-receiving layercoating solution. Particularly useful hardening agents are acroleincondensates, such as that sold by Shell Development Corporation underthe trade name Aldocryl Resin X-12, and disclosed in the copendingapplication of Lloyd D. Taylor, Ser. No. 229,- 194, filed Oct. 8, 1962.

In a particularly useful embodiment, the processing composition containsa substantial concentration of potassium ions, e.g., at least 50% andmore preferably at least 75 to of the alkali metal ions (by weight)present are potassium ions. Use of such potassium containing processingcompositions has effected a substantial reduction in imbibition time inprocesses of the type with which this invention is concerned. When otheralkali metal ions also are present, e.g., sodium, lithium, or cesium,particularly useful r sults are obtained when at least part of suchadditional alkali metal ions are lithium ions, and the lithium ionconcentration preferably is from 1 to 15%, by weight, of the totalalkali metal ions present. In general, it may be said that potassiumhydroxide is used in a concentration at least equivalent to the normallyused sodium hydroxide concentrations, the pH of the processingcomposition being of the order of at least pH 12 to 14. Useful resultsmay be obtained by the use of potassium hydroxide concentrations withinthe range of about 2 to 15%, by weight.

Several examples of useful image-receiving elements have been notedabove and in the noted patent and copending applications, e.g.,polyvinyl alcohol or gelatin containing a dye mordant such aspoly-4-vinylpyridine. The image-receiving element also may contain adevelopment restrainer or arrestor, e.g., l-phenyl-5-mercaptotetrazole,as disclosed in the copending application of Howard G. Rogers andHarriet W. Lutes, Ser. No. 50,849, filed Aug. 22, 1960 (now U.S. PatentNo. 3,265,498 issued Aug. 9, 1966).

The symbol pH as used throughout the specification and the attachedclaims represents the logarithm of the reciprocal of the hydrogen ionconcentration. The pH of the transfer image is determined by the use ofpH paper wet with distilled water and measured at the surface of theimage-receiving layer.

The following examples are given for purposes of illustration and arenot intended to be limiting. Unless otherwise indicated, thephotosensitive element employed was a commercially available integralmultilayer negative of the type commercially available under thedesignation Polaroid Polacolor Type 108 Land film; the total thicknessof the various permeable layers coated on the support was approximately0.00075." Concentrations of reagents are given as percent by weight.

EXAMPLE 1 A photosensitive element was exposed to a color step wedge.The exposed photosensitive element was then dipped into a container of anonviscous aqueous alkaline solution containing:

Percent Potassium hydroxide 10.0 N-benzyl-tx-picolinium bromide 2.0Benzotriazole 3 .5 Zinc nitrate 0.5

After 8 seconds, the photosensitive element was r moved from thecontainer and immediately pressed into face-toface contact with a dryimage-receiving element by passing the two elements between pressurerolls adjusted to firmly press them together without squeezing absorbedprocessing solution of the photosensitive element. Any excess liquid onthe surface of the photosensitive element also was removed by the rolls.The image-receiving element prepared by coating cellulose nitratesubcoated baryta paper with a polymeric acid layer approximately0.00075" thick comprising the n-butyl half-ester of poly-(ethylene/maleic anhydride), followed by a spacer layer approximately0.0003" thick comprising polyvinyl alcohol, followed by animage-receiving layer approximately 0.0003" thick comprising a 2:1mixture, by weight, of polyvinyl alcohol and poly-4-vinylpyridine andalso containing a small amount of l-phenyl-5-mercaptotetrazole. Thephotosensitive and image-receiving elements were 11 held in contact for60 seconds, after which they were separated.

EXAMPLE 2 The procedure described in Example 1 Was repeated except thatthe processing solution also contained 0.5% potassium thiosulfate. Theresulting multicolor transfer image exhibited substantially the samecolor balance but a higher exposure index or faster film speed than thetransfer image obtained in Example 1. The integral blue, green and red Hand D curves, taken from the neutral column of the step wedge, of themulticolor transfer image of this example are reproduced in FIG. 3; thefollowing reflection densities were measured in the neutral column:

Blue Green R ed Pictures made in accordance with the procedure describedin this example exhibit better reds, better flesh tones, and at leasttwice the resolution as transfer images prepared using the samephotosensitive element and imagereceiving element and a viscousprocessing composition.

EXAMPLE 3 column:

Blue Green Red Dm 1. 43 1.45 1.38 min 0. 17 0. 09 0. 02

A comparison of the multicolor transfer images obtained in Examples 3and 4 showed that the film speeds were substantially the same, but thatthe transfer image of Example 3 had much better color balance, andgreater densities, particularly the magenta and yellow densities,without increased highlight densities.

EXAMPLE 4 The procedure described in Example 2 was repeated, except thatthe benzotriazole concentration was reduced to 1.5%. The resultingmulticolor transfer image exhibited a lower D and better greens than theimage obtained in Example 2.

EXAMPLE 5 The procedure described in Example 2 was repeated using anonviscous aqueous alkaline processing solution containing:

Percent Potassium hydroxide 10.0 N-benzyl-a-pic0linium bromide 1.0Benzotriazole 1.75 Zinc nitrate 0.25 Potassium thiosulfate 0.25

The resulting multicolor transfer image exhibited greater cyan density.

EXAMPLE 6 The procedure described in Example 2 was repeated, adding 0.5%lithium nitrate to the processing solution. This resulted in improvedcolor balance in room temperature processing, and substantiallyincreased cyan transfer. Very good quality multicolor transfer imageswere made even when the time the photosensitive and image-receivingelements were in face-to-face contact was reduced to 20 seconds.

1 2 EXAMPLE 7 The procedures described in Examples 4 and 5 were repeatedat 45 F., the solution being heated to 72 F. Good transfer images wereobtained when the photosensitive element and image-receiving elementwere in contact for 60 seconds; if this contact time were increased to120 seconds, the resulting multicolor step wedge transfer images weresubstantially similar to those obtained when the transfer was effectedat 72 F. These experiments show that excellent transfer images may beeffected at low temperatures if the initial permeation and developmentare effected at a relatively higher temperature, e.g., room temperature.

' EXAMPLE 8 The procedure described in Example 2 was repeated at atemperature of F. by conditioning all the components for 2 hours at 95F. Very good transfer images were obtained with the photosensitiveelement dipped into the processing solution for 6 seconds, employing animbibition or transfer time of 60 seconds.

EXAMPLE 9 When the procedure described in Example 8 was repeated at 50F., good transfer images were obtained by dipping the photosensitiveelement into the solution for 15 seconds, and allowing thephotosensitive and image receiving elements to imbibe for seconds.Addition of 0.5% lithium nitrate to the processing solution permittedshortening the time the photosensitive element was in the solution to 12seconds.

EXAMPLE 10 The procedure described in Example 2 was repeated with allcomponents conditioned at 72 F., but the superposed photosensitiveelement and image-receiving element were immediately subjected to atemperature of 43 F. The transfer image obtained in 60 seconds in thismanner exhibited only very slightly less density, primarily cyandensity, than the transfer image obtained when imbibition was effectedat 72 F. This example, like Example 7. shows the importance of thetemperature at which development is initiated.

Experiments using the commercially available photosensitive element ofPolaroid Polacolor Type 108 Land film and the image-receiving element ofExample 1 show that good results can be obtained if the photosensitiveelement is allowed to contact the processing solution for a period ofabout 4 to 15 seconds, and the thusimpregnated photosensitive element isheld in face-to-face contact with the image-receiving element for aperiod of about 15 to 120 seconds; longer imbibition times do notsignificantly change transfer density or color balance. Longer contacttimes of the photosensitive element with the processing solution mayresult in reduced transfer image density, particularly yellow density,while if this time is shorter, the transfer image density, primarilycyan, is reduced, and this reduced density is not brought back by longerimbibition.

Twenty-four (24) photosensitive elements, each 2%" x 2%", of the typeused in Example 2 were dipped in the processing solution of Example 2for 8 seconds each. The Wet negatives were weighed after being removedand passed through the rollers (Without the image-receiving element).The solution left in the container after all 24 negatives had beentreated also was weighed. It was found that each 2%" x 2%" negativeabsorbed an average of approximately 0.268 g. or 0.25 cc. of theprocessing solution. This is substantially less than the amount ofsolution available in the commercially practised viscous solutionembodiment, wherein 0.95 g. of viscous reagent is used to process animage area of 2%" x 3 /8", approximately 60-75% of this reagent beingretained between the image areas of the negative and positive sheets.

It will be understood that this invention may be utilized to processindividual sheets of film, or it may be employed 13 in continuousprocessing of long strips of film, e.g., movie film. The sheet materialsemployed may be substantially plain sheets or webs, requiring none ofthe masks, traps, containers or other arrangements for providing theprocessing liquid, controlling the distribution of the processingcomposition, or the trapping and retaining of the processingcomposition, as are utilized with viscous processing solutions. Ifdesired, a white border on the transfer image may be provided by a whitelight exposure of a marginal strip of each frame prior to photoexpsoure,or by other techniques obvious to one skilled in the art.

Since certain changes may be made in the above processes withoutdeparting from the scope of the invention here involved, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. 7

What is claimed is:

1. A diffusion transfer process for forming a transfer image in color,comprising the steps of: (a) exposing a photosensitive elementcontaining at least one silver halide emulsion, each said silver halideemulsion having associated therewith a dye developer; (b) contactingsaid exposed photosensitive element with a nonviscous aqueous alkalineprocessing solution for a short period whereby a relatively smallquantity of said processing solution is absorbed by said exposedphotosensitive element and development of said exposed photosensitiveelement is thereby initiated; (c) bringing said exposed photosensitiveelement containing said absorbed processing solution into face-to-facecontact with a dry image-receiving element, said image-receiving elementincluding an image-receiving layer and a non-diffusible, acid-reactingreagent positioned in a layer adjacent to said image-receiving layer;(d) forming, as a function of said development, an imagewisedistribution of diffusible dye developer in undeveloped areas of eachsaid silver halide emulsion, and transferring at least a portion of eachsaid imagewise distribution of diffusible dye developer, by diffusion,to said image-receiving layer to form said transfer image in color, saidabsorbed small quantity of processing composition being sufficient toeffect said development and said transfer, said exposed photosensitiveelement containing said absorbed processing solution being pressed intofaceto-face contact with said dry image-receiving element before anysignificant quantity of dye developer has diffused out of saidphotosensitive element.

2. A diffusion transfer process as defined in claim 1, wherein saidperiod during which said exposed photosensitive element is in contactwith said processing solution is substantially less than the periodduring which said exposed photosensitive element is in contact with saidimage-receiving element.

3. A diffusion transfer process as defined in claim 1, wherein saidphotosensitive element contains a layer of a blue-sensitive silverhalide emulsion, a layer of a greensensitive silver halide emulsion, anda layer of, a redsensitive silver halide emulsion, said silver halideemulsions being superposed on the same support and having associatedtherewith, respectively, a yellow dye developer, a magenta dyedeveloper, and a cyan dye developer, each of said dye developerscontaining a hydroquinonyl radical.

4. A diffusion transfer process as defined in claim 1, wherein an inert,alkali-permeable layer is positioned between said image-receiving layerand said layer containing a non-diffusible, acid-reacting reagent.

5. A diffusion transfer process as defined in claim 1, wherein saidnon-diffusible, acid-reacting reagent is a polymeric acid.

6. A diffusion transfer process as defined in claim 1, wherein thereaction of said non-diffusible, acid-reacting reagent with alkalireleases water.

7. A diffusion transfer process for forming a transfer image in color,comprising the steps of: (a) exposing a photosensitive elementcontaining at least one silver halide emulsion, each said silver halideemulsion having associated therewith a dye developer; (b) absorbing arelatively small quantity of a non-viscous processing solution into saidexposed photosensitive element, thereby initiating development of saidexposed photosensitive element; (c) bringing said exposed photosensitiveelement containing said absorbed processing solution into face-tofacecontact with a dry image-receiving element, said image-receiving elementincluding an image-receiving layer and a non-diffusible, acid-reactingreagent positioned in a layer adjacent to said image-receiving layer;(d) forming, as a function of said development, an imagewisedistribution of diffusible dye developer in undeveloped areas of eachsaid silver halide emulsion, and transferring at least a portion of eachsaid imagewise distribution of diffusible dye developer, by diffusion,to said image-receiving layer to form said transfer image in color, saidabsorbed small quantity of processing composition Eeing sufficient toeffect said development and said trans- 8. A diffusion transfer processfor forming a multicolor transfer image, comprising the steps of: (a)exposing a photosensitive element comprising a layer of a bluesensitivesilver halide emulsion, a layer of a green-sensitive silver halideemulsion, and a layer of a red-sensitive silver halide emulsion, saidsilver halide emulsions being superposed on the same support and havingassociated therewith, respectively, a yellow dye developer, 9. magentadye developer, and a cyan dye developer; (b) passing said exposedphotosensitive element through a nonviscous aqueous alkaline processingsolution at a rate such that a relatively small quantity of saidprocessing solution is absorbed by said exposed photosensitive elementand development of said exposed photosensitive element is therebyinitiated; (c) bringing said exposed photosensitive element containingsaid absorbed processing solution into face-to-face contact with a dryimage-receiving element, said image-receiving element including animage-receiving layer and a layer containing a polymeric acid positionedbetween the support and said imagereceiving layer; (d) forming, as afunction of said development, an imagewise distribution of diffusibledye developer in undeveloped areas of each said silver halide emulsion,and transferring at least a portion of each said imagewise distributionof diffusible dye developer, by diffusion, to said image-receiving layerto form said multicolor transfer image, said absorbed small quantity ofprocessing composition being sufficient to effect said development andsaid transfer.

9. A diffusion transfer process as defined in claim 8, wherein saidexposed photosensitive element is in said processing solution for aperiod of about 4 to 15 seconds, after which it is immediately broughtinto said face-to-face contact with said dry image-receiving element.

10. A diffusion transfer process as defined in claim 9, wherein saidphotosensitive element and said image-receiving element are maintainedin said face-to-face contact for a period of about 15 to seconds.

11. A diffusion transfer process as defined in claim 8, wherein saidaqueous alkaline processing composition has a pH of at least 12, andsaid polymeric acid is present in a quantity sufficient to reduce the pHof the imagereceiving layer to less than 8.

12. A diffusion transfer process for forming a transfer image in color,comprising the steps of: (a) exposing a photosensitive elementcontaining at least one silver halide emulsion, each said silver halideemulsion having associated therewith a dye developer; (b) absorbing arelatively small quantity of a processing solution into said exposedphotosensitive element, thereby initiating development of said exposedphotosensitive element; (c) bringing said exposed photosensitive elementcontaining said absorbed processing solution into face-to-face contactwith a dry image-receiving element, said image-receiving elementincluding an image-receiving layer and a non-difiusible, acid reactingreagent positioned in a layer adjacent to said image-receiving layer;(d) forming, as a function of said development, an imagewisedistribution of diffusible dye developer in undeveloped areas of eachsaid silver halide emulsion, and transferring at least a portion of eachsaid imagewise distribution of diffusible dye developer, by ditfusion,to said image-receiving layer to form said transfer image in color, saidabsorbed small quantity of processing composition being sufficient toeffect said development and said transfer, said diffusion transfer beingperformed at a temperature which is lower than the temperature of saidprocessing solution when said processing solution is absorbed into saidphotosensitive element.

References Cited UNITED STATES PATENTS 1,907,252 5/1933 Debrie 96482,500,421 3/1950 Land 9629 5 3,345,172 10/1967 Land 9648 3,362,8191/1968 Land 963 3,362,821 1/1968 Land 9629 NORMAN G. TORCHIN, PrimaryExaminer A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 963

